Semiconductor laser array

ABSTRACT

A semiconductor laser array includes a plurality of stripe-shaped stimulated regions of the index guide type. A plurality of buried layers are disposed between each of the plurality of stripe-shaped stimulated regions. A light absorption layer is formed in each of the plurality of stripe-shaped stimulated regions so that the stimulated region has the optical loss greater than an buried layer, whereby optical coupling is performed with no phase difference.

This application is a continuation of application Ser. No. 07/390,511filed on Aug. 7, 1989, now abandoned, which is a Reissue of Ser. No.06/730,747, now U.S. Pat. No. 4,723,253.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor laser and, moreparticularly, to a semiconductor laser array which includes a pluralityof stripe-shaped stimulated regions. The plurality of stripe-shapedstimulated regions are phase-coupled to each other so that the laserbeams are coupled to each other with a phase difference of zero degrees,thereby obtaining a high power laser beam.

2. Description of the Related Art

A semiconductor laser has widely been used as a light source in anoptical information processing system such as an optical communicationsystem and a digital audio disc system. Further, the semiconductor laseris widely used in an optical disc system wherein new information can bewritten into the optical memory disc through the use of a semiconductorlaser, the output power of which is modulated in accordance with theinformation to be written into the optical memory disc. Rapid processingis required in such an optical information processing system as theamount of information to be handled increases. To ensure the rapidprocessing, the semiconductor laser must emit the laser beam at a highpower level in a stable operating range. However, in the conventionalsemiconductor laser having a single stimulated region, the practicalmaximum output is about 40 mW.

To enhance the output level, a semiconductor laser array has beenproposed, wherein a plurality of stimulated regions are aligned in aparallel fashion, and the plurality of stimulated regions are optically,phase coupled to each other so as to emit the laser beam in a singlephase. This is referred to as a phase coupled laser array. The phasecoupled semiconductor laser array is effective to converge the laserbeams in a narrow radiation angle.

In the conventional semiconductor laser array of the gain guide type,the gain is substantially reduced at the coupling region positionedbetween two adjacent laser emitting regions and, therefore, the electricfield has a phase difference of 180 degrees at two adjacent laseremitting regions. The far field pattern has a plurality of peaks asshown in FIG. 8. Thus, the conventional semiconductor laser array of thegain guide type cannot be of practical use.

To improve the above-mentioned problems, a semiconductor laser array ofthe index guide type has been proposed. For example, D. E. Ackley et alof Hewlett-Packard Laboratories proposed a semiconductor laser array ofa buried heterostructure laser with a leaky mode (Appl. Phys. Letters,vol. 39, 1981, pp. 27). The proposed laser array ensures an effectivecoupling of the laser emitting regions, but has two peaks in the farfield pattern because of the leaky mode.

D. Botez et al of RCA Laboratories proposed a CSP-LOC(Channeled-Substrate-Large-Optical-Capacity) laser (document of IOOC,1983, 29B5-2). The proposed semiconductor laser utilizes thedistribution of effective refractive index which is formed by a couplingto the GaAs substrate. The region disposed between two adjacent laseremitting regions has a high absorption coefficient. The refractive indexdifference is not obtained when the absorption coefficient is minimized.Accordingly, it is difficult to reduce the phase difference between twoadjacent laser emitting regions to zero.

D. E. Ackley et al of Hewlett-Packard Laboratories further proposed thesemiconductor laser array of the ridge-type (Appl. Phys. Letters, vol.42, 1983, pp. 152). Each pair of adjacent laser emitting regions has aphase difference of 180 degrees of the high absorption caused by anelectrode disposed at a coupling region of the adjacent laser emittingregions.

OBJECTS AND SUMMARY OF THE INVENTION Objects of the Invention

Accordingly, an object of the present invention is to provide asemiconductor laser array which ensures a stable operation and a highpower output.

Another object of the present invention is to provide a semiconductorlaser array of the index guide type, wherein the laser emitting regionsare coupled to each other with a phase difference of zero degrees.

Other objects and further scope of applicability of the presentinvention will become apparent from the detailed description givenhereinafter. It should be understood, however, that the detaileddescription and specific examples, while indicating preferredembodiments of the invention, are given by way of illustration only,since various changes and modifications within the spirit and scope ofthe invention will become apparent to those skilled in the art from thisdetailed description.

Summary of the Invention

To achieve the above objects, pursuant to an embodiment of the presentinvention, a plurality of stripe-shaped stimulated regions are formed ina semiconductor substrate in a parallel fashion. An optical loss isadded to each of the plurality of stimulated regions so thatstripe-shaped stimulated region has an optical loss greater than that ofthe coupling regions disposed between adjacent stripe-shaped stimulatedregions, whereby the phase difference between the adjacent stimulatedregions is held at zero degrees. The laser emission is carried out at ahigh power level in a stable operating range.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be better understood from the detaileddescription given hereinbelow and the accompanying drawings which aregiven by way of illustration only, and thus are not limitative of thepresent invention and wherein:

FIG. 1 is a sectional view of an embodiment of a semiconductor laserarray of the present invention;

FIGS. 2,3,4 and 5 are sectional views for explaining manufacturing stepsof the semiconductor laser array of FIG. 1;

FIG. 6 is a graph showing the far field pattern obtained by thesemiconductor laser array of FIG. 1;

FIG. 7 is a sectional view of another embodiment of a semiconductorlaser array of the present invention; and

FIG. 8 is a graph showing the far field pattern of a semiconductor laserarray of the conventional gain guide type.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The semiconductor laser array of the present invention includes ann-GaAs substrate 1, and an n-Ga₀.6 Al₀.4 As cladding layer 2 formed onthe n-GaAs substrate 1. A p-Ga₀.9 Al₀.1 As active layer 3 is formed onthe n-Ga₀.6 Al ₀.4 As cladding layer 2, and a p-Ga₀.6 Al₀.4 As claddinglayer 4 is formed on the p-Ga₀.9 Al₀.1 As active layer 3. Stripe-shapedthick portions 4a, each having a width of, for example, 3 μm, are formedin the p-Ga₀.6 Al₀.4 As cladding layer 4 with a distance of, forexample, 7 μm. On the thick portions 4a, a p-GaAs light absorption layer5, a p-Ga₀.6 Al₀.4 As cladding layer 6, and a p-GaAs cap layer 7 areformed.

An n-Ga₀.5 Al₀.5 As buried layer 9 is formed on the p-Ga₀.6 Al₀.4 Ascladding layer 4 at the positions where the thick portions 4a are notformed, in a manner that the top surface of the n-Ga₀.5 Al₀.5 As buriedlayer 9 substantially has the same height as the top surface of thep-GaAs cap layer 7. An oxide film 10 is formed on the top surface of then-Ga₀.5 Al₀.5 As buried layer 9. A Cr/Au electrode 11 commonly formed onthe p-GaAs cap layer 7 and the oxide film 10. An AuGe/Ni electrode 12 isformed on the bottom surface of the n-GaAs substrate 1. The n-Ga₀.6Al₀.4 As cladding layer 2, p-Ga₀.9 Al₀.1 As active layer 3, p-Ga₀.6Al₀.4 As cladding layer 4, p-GaAs light absorption layer 5, p-Ga₀.6Al₀.4 As cladding layer 6, and p-GaAs cap layer 7 form, in combination,stripe-shaped stimulated regions 13.

The p-GaAs light absorption layer 5 and the p-Ga₀.6 Al₀.4 As claddinglayer 6 in each stripe-shaped stimulated region 13 have the greaterrefractive index than the n-Ga₀.5 Al₀.5 As buried layer 9, therebyforming the semiconductor laser of the index guide type. Each of thestripe-shaped stimulated regions 13 includes the p-GaAs light absorptionlayer 5 and, therefore, the optical loss in the stripe-shaped stimulatedregions 13 is greater than that in the n-Ga₀.5 Al₀.5 As buried layer 9.With this structure, the optical loss in the n-Ga₀.5 Al₀.5 As buriedlayer 9 is small as compared with the optical loss in the stripe-shapedstimulated regions 13 and, therefore, the laser beams generated fromeach of the stripe-shaped stimulated regions 13 are coupled to eachother with no phase difference in a stable operational mode.

Manufacturing steps of the semiconductor laser array of FIG. 1 will bedescribed with reference of FIGS. 2, 3, 4 and 5.

The n-Ga₀.6 Al₀.4 As cladding layer 2 of 1 μm thick, the p-Ga₀.9 Al₀.1As active layer 3 of 0.1 μm thick, the p-Ga₀.6 Al₀.4 As cladding layer 4of 0.3 μm thick, the p-GaAs light absorption layer 5 of 0.05 μm thick,the p-Ga₀.6 Al₀.4 As cladding layer 6 of 0.7 μm thick, and the p-GaAscap layer 7 of 0.3 μm thick are sequentially formed on the n-GaAssubstrate 1 through the use of the liquid-phase epitaxial growth methodas shown in FIG. 2.

Then, stripe-shaped resists 8 are formed on the p-GaAs cap layer 7through the use of the photolighography technique. The thus formedresists 8 function as the masks in the following etching operation. Thep-GaAs cap layer 7 and the p-Ga₀.6 Al₀.4 As cladding layer 6 are removedby the etching method at the position where the stripe-shaped resists 8are not formed, as shown in FIG. 3. The etching operation first uses anetchant consisting of H₂ SO₄, H₂ O₂ and H₂ O (H₂ SO₄ :H₂ O₂ :H₂O=10:1:1) which is capable of etching both GaAs and GaAlAs evenly. Theetching operation is conducted to a depth that at least reaches thep-Ga₀.6 Al₀.4 As cladding layer 6. Thereafter, the etching operation iscarried out through the use of hydrofluoric acid (HF), which is capableof selectively etching GaAlAs, to etch the remaining p-Ga₀.6 Al₀.4 Ascladding layer 6.

After completion of the etching operation, the stripe-shaped resists 8are removed, and a meltback etching using an unsaturated solution iscarried out in a liquid-phase growth board. The p-GaAs light absorptionlayer 5 is removed at the positions where the p-Ga₀.6 Al₀.4 As claddinglayer 6 is removed by the preceding etching operation. The meltbacketching is carried out to the depth where the p-Ga₀.6 Al₀.4 As claddinglayer 4 is slightly removed. Then, the n-Ga₀.5 Al₀.5 As buried layer 9is formed on the semiconductor body as shown in FIG. 4. In a preferredform, each of the stripe-shaped resists 8 has the width of 3 μm, and thestripe-shaped resists 8 are formed with a pitch of 7 μm.

An etching operation is carried out to the depth at which the p-GaAs caplayer 7 appears as shown in FIG. 5 through the use of hydrofluoric acid(HF) diluted by acetic acid. The native oxide 10 is formed on the n-Ga₀.5 Al₀.5. As buried layer 9 while the etching operation is conducted.Finally, the Cr/Au electrode 11 is formed on the p-GaAs cap layer 7 andthe native oxide 10. Further, the AuGe/Ni electrode 12 is formed on thebottom surface of the n-GaAs substrate 1.

FIG. 6 shows the far field pattern when a semiconductor laser array ofthe above-mentioned structure and having seven (7) stripe-shapedstimulated regions 13 is driven at the threshold current of 210 mA, andthe output power above 100 mW. The single peak far field patternindicates a stable operation of the semiconductor laser array of thepresent invention.

In the foregoing embodiment, the n-Ga₀.5 Al₀.5 As buried layer 9function to confine the electric current in the stripe-shaped stimulatedregions 13. In order to increase the gain, a p-Ga₀.5 Al₀.5 As buriedlayer can be employed. In this case, the native oxide 10 functions toconfine the electric current in the stripe-shaped stimulated regions 13.If the layers shown in FIG. 2 are formed by, for example, the MBE methodor the MO-CVD method, which ensures fine control of the layer thickness,instead of the liquid-phase epitaxial growth method, the indexdifference and the loss difference can be accurately controlled betweenthe stripe-shaped stimulated regions 13, including the p-GaAs lightabsorption layer 5 and the p-Ga₀.6 Al₀.4 As cladding layer 6, and then-Ga₀.5 Al₀.5 As buried layer 9.

FIG. 7 shows another embodiment of a semiconductor laser array of thepresent invention.

Mesas 20, each having a predetermined width, are formed on an n-GaAssubstrate 21 with a predetermined pitch. An n-Ga₀.7 Al₀.3 As claddinglayer 22, a p-GaAs active layer 23, a p-Ga₀.7 Al₀.3 As cladding layer24, and an n-GaAs cap layer 25 are sequentially formed on the n-GaAssubstrate 21. A Zn diffusion is conducted to the portions correspondingto the mesas 20 to reach the p-Ga₀.7 Al₀.3 As cladding layer 24, therebyforming current paths 26. A first electrode 27 is formed on the n-GaAscap layer 25, and a second electrode 28 is formed on the bottom surfaceof the n-GaAs substrate 21.

The thickness of the p-GaAs active layer 23 varies depending on theprovision of the mesas 20. More specifically, the thickness of thep-GaAs active layer 23 is maximum at the center of the mesa 20, and isminimum between the mesas 20. Accordingly, the stripe-shaped stimulatedregions 13 of the index guide type are formed above the mesas 20. Then-Ga₀.7 Al₀.3 As cladding layer 22 is thin, for example, about 0.5 μm,at the center of the mesas 20 so as to increase the optical loss in thestrip-shaped stimulated regions 13 by absorbing the laser beam by then-GaAs substrate 21 via the mesas 20.

The semiconductor laser array of FIG. 7 is manufactured in the followingmanner. The mesas 20 are formed on the n-GaAs substrate 21 through theuse of the photolithography method and the chemical etching method. Eachof the mesa 20 preferably has the width of about 2.5 μm, and the heightof about 1 μm. The n-Ga₀.7 Al₀.3 As cladding layer 22 is formed on then-GaAs substrate 21 by the liquid-phase epitaxial growth method. Then-Ga₀.7 Al₀.3 As cladding layer 22 has the thickness of about 0.5 μm atthe center of the mesas 20. Then, the p-GaAs active layer 23 is formedon the n-Ga₀.7 Al₀.3 As cladding layer 22 by the liquid-phase epitaxialgrowth method. The p-GaAs active layer 23 has a thickness of about 0.12μm at the center of the mesas 20. The cladding layer 24 having athickness of about 1 μm, and the n-GaAs cap layer 25 having a thicknessof about 0.5 μm are sequentially formed by the liquid-phase epitaxialgrowth method. Then, the Zn diffusion is conducted at the positioncorresponding to the mesas 20 so that the Zn diffusion reaches thecladding layer 24, thereby forming the current paths 26. Finally, theelectrode 27 is formed on the n-GaAs cap layer 25, and the electrode 28is formed on the bottom surface of the n-GaAs substrate 21.

The present invention is applicable to an InGaAsP semiconductor laser oran InGaAlP semiconductor laser in addition to the GaAlAs semiconductorlaser.

The invention being thus described, it will be obvious that the same maybe varied in many ways without departure from the spirit and scope ofthe invention, which is limited only by the following claims.

What is claimed is:
 1. A semiconductor element in a semiconductor laserarray comprising:a semiconductor substrate; a plurality of stripe-shapedstimulated regions of an index guide type formed on said semiconductorsubstrate; a plurality of buried layers, a buried layer being disposedbetween adjacent ones of said plurality of stripe-shaped stimulatedregions, wherein said plurality of stripe-shaped stimulated regionscomprise a light absorption layer so that said plurality ofstripe-shaped stimulated regions have an optical loss greater than anoptical loss of said plurality of buried layers; a first electrodeformed commonly on said plurality of stripe-shaped stimulated regions;and a second electrode formed on a bottom surface of said semiconductorsubstrate.
 2. A semiconductor laser array comprising:a semiconductorsubstrate; a first cladding layer formed on said semiconductorsubstrate; an active layer formed on said first cladding layer; a secondcladding layer formed on said active layer; a plurality of stripe-shapedstimulated regions formed on said second cladding layer, each of saidplurality of stripe-shaped stimulated regions including:a lightabsorption layer formed on said second cladding layer; a third claddinglayer formed on said light absorption layer; and a cap layer formed onsaid third cladding layer: a plurality of buried layers disposed betweeneach of said plurality of stripe-shaped stimulated regions; a pluralityof oxide films formed on each of said plurality of buried layers; afirst electrode formed commonly on said plurality of stripe-shapedstimulated regions and said plurality of oxide films; and a secondelectrode formed on the bottom surface of said semiconductor substrate.3. A GaAlAs semiconductor laser array comprising:an n-GaAs substrate; Ann-Ga₀.6 Al₀.4 As cladding layer formed on said n-GaAs substrate; ap-Ga₀.9 Al₀.1 As active layer formed on said n-Ga₀.6 Al₀.4 As claddinglayer; a p-Ga₀.6 Al₀.4 As cladding layer formed on said p-Ga₀.9 Al₀.1 Asactive layer; a plurality of stripe shaped stimulated regions formed onsaid p-Ga₀.6 Al₀.4 As cladding layer, each of said plurality ofstripe-shaped stimulated regions including:p-GaAs light absorption layerformed on said p-Ga₀.6 Al₀.4 As cladding layer; a p-Ga₀.6 Al₀.4 Ascladding layer formed on said p-GaAs light absorption layer; and ap-GaAs cap layer formed on said p-Ga₀.6 Al₀.4 As cladding layer; aplurality of n-Ga₀.5 Al₀.5 As buried layers disposed between each ofsaid plurality of stripe-shaped stimulated regions; a plurality of oxidefilms formed on each of said plurality of n-Ga₀.5 AL₀.5 As buriedlayers; a first electrode formed commonly on said plurality ofstripe-shaped stimulated regions and said plurality of oxide films; anda second electrode formed on the bottom surface of said n-GaAssubstrate.
 4. The semiconductor element of claim 1 wherein each of saidplurality of stripe-shaped stimulated regions formed on saidsemiconductor substrate further comprise:a cladding layer disposed onsaid light absorption layer; and a cap layer formed on said claddinglayer.
 5. The semiconductor element of claim 4 further comprising aplurality of oxide films each oxide film being disposed on one of saidplurality of buried layers.
 6. The semiconductor laser array of claim 2wherein said third cladding layer has a refractive index greater thaneach of said plurality of buried layers.
 7. The semiconductor laserarray of claim 2 wherein each of said stripe-shaped stimulated regionshave an optical loss greater than an optical loss of said plurality ofburied layers.
 8. The semiconductor laser array of claim 2 wherein eachof said plurality of buried layers includes n-Ga₀.5 Al₀.5 As.
 9. Thesemiconductor laser array of claim 2 wherein each of said plurality ofburied layers includes p-Ga₀.5 Al₀.5 As. .Iadd.
 10. A semiconductorlaser device comprising:a semiconductor substrate; first cladding layerformed on said semiconductor substrate; an active layer formed on saidfirst cladding layer; a second cladding layer formed on said activelayer and having an area coextensive with a portion of said activelayer; a light absorption layer formed on said second cladding layerover said coextensive area; a third cladding layer formed on andcoextensive with said light absorption layer; a cap layer formed on andcoextensive with said third cladding layer; and a buried layer formed onsaid second cladding layer of a thickness subtending said lightabsorption layer, said third cladding layer and said cap layer..Iaddend. .Iadd.11. The laser device of claim 10, wherein said lightabsorption layer and said third cladding layer have a refractive indexgreater than that of said buried layer. .Iaddend. .Iadd.12. The laserdevice of claim 10, which further includes a first electrode layer onsaid substrate opposite said first cladding layer; and a secondelectrode layer on said cap layer. .Iaddend. .Iadd.13. The laser deviceof claim 12, wherein said third cladding layer has a refractive indexgreater than that of said buried layer. .Iaddend. .Iadd.14. The laserdevice of claim 10, wherein said coextensive area of said secondcladding layer is of equal or greater thickness than the remainderthereof. .Iaddend. .Iadd.15. The laser device of claim 14, wherein saidlight absorption layer and said third cladding layer have a refractiveindex greater than that of said buried layer. .Iaddend. .Iadd.16. Thelaser device of claim 14, which further includes a first electrode layeron said substrate opposite said first cladding layer; anda secondelectrode layer on said cap layer. .Iaddend. .Iadd.17. The laser deviceof claim 16, wherein said third cladding layer has a refractive indexgreater than that of said buried layer. .Iaddend. .Iadd.18. Asemiconductor laser device comprising: a semiconductor substrate ofn-GaAs; a first cladding layer of n-Ga₀.6 Al₀.4 As formed on saidsubstrate; an active layer of p-Ga₀.9 Al₀.1 As formed on said firstcladding layer; a second cladding layer of p-Ga₀.6 Al₀.4 As formed onsaid active layer and having an area coextensive with a portion of saidactive layer; a light absorption layer of p-GaAs formed on said secondcladding layer over said coextensive area; a third cladding layer ofp-Ga₀.6 Al₀.4 As formed on and coextensive with said light absorptionlayer; a cap layer of p-GaAs formed on and coextensive with said thirdcladding layer; and a buried layer of n-Ga₀.5 Al₀.5 As formed on saidsecond cladding layer of a thickness subtending said light absorptionlayer, said third cladding layer and said cap layer. .Iaddend. .Iadd.19.The laser device of claim 18, which further includes a first electrodelayer on said substrate opposite said first cladding layer; anda secondelectrode layer on said cap layer. .Iaddend. .Iadd.20. The laser deviceof claim 18, wherein said coextensive area of said second cladding layeris of equal or greater thickness than the remainder thereof. .Iaddend..Iadd.21. The laser device of claim 20, which further includes a firstelectrode layer on said substrate opposite said first cladding layer;and a second electrode layer on said cap layer. .Iaddend. .Iadd.22. Themethod of manufacturing a semiconductor laser device comprising thesteps of:providing a substrate of semiconductor material; sequentiallyforming a first cladding layer on said substrate, an active layer onsaid first cladding layer, a second cladding layer on said active layer,a light absorption layer on said second cladding layer, a third claddinglayer on said light absorption layer and a cap layer on said thirdcladding layer; forming a mask on said cap layer; applying a firstetchant to said cap layer to remove the unmasked portions of said caplayer and at least some of the corresponding portions of said thirdcladding layer; applying a second etchant to said third cladding layerto remove the remainder of said corresponding portions and expose saidlight absorption layer; applying a third etchant to said lightabsorption layer to remove portions thereof corresponding to removedportions of said third cladding layer down to said second claddinglayer; removing said mask; forming a buried layer on said cladding layerto a depth at least subtending the combined thickness of said lightabsorption layer, said third cladding layer and said cap layer; andapplying a fourth etchant to said buried layer and said cap layer toreduce the thickness of said cap layer. .Iaddend. .Iadd.23. The methodof claim 22, which further includes the steps of:forming a firstelectrode on said cap layer; and forming a second electrode on saidsemiconductor substrate opposite said first cladding layer. .Iaddend..Iadd.24. The method of claim 22, which further includes utilizing saidthird etchant to remove some of said second cladding layer, leaving athicker portion thereof in the shape of said mask overlying said activelayer. .Iaddend. .Iadd.25. The method of claim 24, which furtherincludes the steps of: forming a first electrode on said cap layer andsaid oxide layer; and forming a second electrode on said semiconductorsubstrate opposite said first cladding layer. .Iaddend. .Iadd.26. Themethod of manufacturing a semiconductor laser array comprising the stepsof: providing a substrate of semiconductor material; sequentiallyforming a first cladding layer on said substrate, an active layer onsaid first cladding layer, a second cladding layer on said active layer,a light absorption layer on said second cladding layer, a third claddinglayer on said light absorption layer and a cap layer on said thirdcladding layer; forming a mask on said cap layer comprising a pluralityof parallel stripe-shaped resists; applying a first etchant to said caplayer to remove the unmasked portions of said cap layer and at leastsome of the corresponding portions of said third cladding layer;applying a second etchant to said third cladding layer to remove theremainder of said corresponding portions and expose said lightabsorption layer; applying a third etchant to said light absorptionlayer to remove portions thereof corresponding to removed portions ofsaid third cladding layer down to said second cladding layer; removingsaid mask; forming a buried layer on said second cladding layer to adepth at least subtending the combined thickness of said lightabsorption layer, said third cladding layer and said cap layer; andapplying a fourth etchant to said buried layer and said cap layer toreduce the thickness of said cap layer. .Iaddend. .Iadd.27. The methodof claim 26, which further includes the steps of:forming a firstelectrode on said cap layer; and forming a second electrode on saidsemiconductor substrate opposite said first cladding layer. .Iaddend..Iadd.28. The method of claim 26, which further includes utilizing saidthird etchant to remove some of said second cladding layer, leaving athicker portion thereof in the shape of said mask overlying said activelayer. .Iaddend. .Iadd.29. The method of claim 28, which furtherincludes the steps of: forming a first electrode on said cap layer; andforming a second electrode on said semiconductor substrate opposite saidfirst cladding layer. .Iaddend. .Iadd.30. The method of manufacturing asemiconductor laser device comprising the steps of:providing a substrateof semiconductor material; sequentially forming a first cladding layeron said substrate, an active layer on said first cladding layer, asecond cladding layer on said active layer, a light absorption layer onsaid second cladding layer, a third cladding layer on said lightabsorption layer and a cap layer on said third cladding layer; forming amask on said cap layer; applying a first etchant to said cap layer toremove the unmasked portions of said cap layer and at least some of thecorresponding portions of said third cladding layer; applying a secondetchant to said third cladding layer to remove the remainder of saidcorresponding portions and expose said light absorption layer; etchingsaid light absorption layer to remove portions thereof corresponding toremoved portions of said third cladding layer down to said secondcladding layer; removing said mask; forming a buried layer on saidcladding layer to a depth at least subtending the combined thickness ofsaid light absorption layer, said third cladding layer and said caplayer; and applying a third etchant to said buried layer and said caplayer to reduce the thickness of said cap layer. .Iaddend. .Iadd.31. Themethod of claim 30 wherein said light absorption layer is etched by ameltback etching technique. .Iaddend.